Five-level active NPC converter topology: SHE-PWM control and operation principles

The neutral-point-clamped (NPC) inverter topology has been the centre of research and development effort for numerous applications, including medium- and high-voltage electric motor drives, static compensators (STATCOMs) and other utility type of power electronic systems for almost three decades now. Pulse-width modulation (PWM) control methods have been developed for such topology for respective three-level and multilevel versions. The issue of voltage balancing between the DC bus capacitors is a drawback that requires attention and the problem becomes more serious as the number of levels increases. Selective harmonic elimination PWM can be applied to control the topology as a method to reduce the switching transitions to the lowest possible number. The active NPC (ANPC) topology is derived from the NPC topology by adding an active switch in anti-parallel to each clamping diode. Hybrid configurations combining flying capacitors are also possible. The five-level topology discussed in this paper is derived through different connections of active clamping paths. A novel recently proposed five-level symmetrically defined SHE-PWM method is applied. The simulation results presented in the paper confirm the suitability of the new method.